python subprocess error calling java class

Question

I'm trying to run a java class from a python script with subprocess.call():

import os
import subprocess
java_file = os.getcwd() + "/src/ch/idsia/scenarios/Main.java"
if os.path.isfile(java_file):
 java_class, _ = os.path.splitext(java_file)
 cmd = ['java', java_class]
 subprocess.call(cmd, shell=False)

But running this python script gives me Error: Could not find or load main class .Users.alavin.Code.MarioAI_ver02_April_2011.src.ch.idsia.scenarios.Main. I've also tried the following variations for java_class: "Users.alavin.Code.MarioAI_ver02_April_2011.src.ch.idsia.scenarios.Main" "src.ch.idsia.scenarios.Main"

The python script is located in "Users/alavin/Code/MarioAI_ver02_April_2011/". The java class is "Main.java" in package "src.ch.idsia.scenarios". The java project is in Eclipse.

Notes: mac osx 10.9; python 2.7; java 1.7; using jython is not an option; running echo $CLASSPATH from the terminal gives a blank line.

Thank you in advance for any help/guidance.

• mhawke: Isn't it a matter of setting the class path appropriately?
• Kashyap: Read up what classpath is. Make sure Main.class is present in /Users/alavin/Code/MarioAI_ver02_April_2011/src/ch/idsia/scenarios/
• BoltzmannBrain: @thekashyap Main.class is in /Users/alavin/Code/MarioAI_ver02_April_2011/bin/ch/idsia/scenarios/. I.e. the .java files in the 'src/' directory have their corresponding .class files in the bin/ directory. Is this a problem?

Answer 1

Try using the -cp option to specify the class path, e.g.

java -cp /Users/alavin/Code/MarioAI_ver02_April_2011/src/ch/idsia/scenarios Main

So,

subprocess.call(['java', '-cp', '/Users/alavin/Code/MarioAI_ver02_April_2011/src/ch/idsia/scenarios', 'Main'])

Edit

Since Main is in package src.ch.idsia.scenarios try amending the command to:

subprocess.call(['java', '-cp', '/Users/alavin/Code/MarioAI_ver02_April_2011', 'src.ch.idsia.scenarios.Main'])

• BoltzmannBrain: I still get Error: Could not find or load main class Main.
• mhawke: Try the revised command. Try running it on the command line to help diagnose any problems.
• BoltzmannBrain: Same error, and running from the command line only returns the value 1. I also tried adding the java program root directory to the python system path with sys.path.append('/Users/alavin/Code/MarioAI_ver02_April_2011'), but still the same error.
• mhawke: Is 1 the expected output? If not then you need to figure out exactly how to run the Java program from the command line and then put that same command into your Python code.
• BoltzmannBrain: 0 is the expected output. Could you please advise how I can run correctly from the command line? I think the issue is with either my CLASSPATH or python system path, or both.

Answer 2

The classpath was the issue; I needed to include the jar files in the call from the terminal: java -cp bin/MarioAI/:lib/asm-all-3.3.jar:lib/jdom.jar ch.idsia.scenarios.Main. So running the subprocess command in python would be:

import subprocess
cmd = ['java', '-cp', 'bin/MarioAI/:lib/asm-all-3.3.jar:lib/jdom.jar', 'ch.idsia.scenarios.Main']
subprocess.call(cmd, shell=False)

To check the jar files in the classpath via Eclipse: right click Main.java -> Run Configurations -> Classpath tab.